Class A surfaces can be defined as any surface, that has styling intent, that is either seen, touched or both.

In an automotive application that means everything on the outside excluding the under body and the interior. This can also include beauty covers in the engine compartment.

In the product realm it can be a hand drill to plastic laundry detergent bottles to kids toys to furniture.

Aerospace has some styling considerations like bezels for air vents and lights.

That is the most basic and expansive of explanation of what a Class A Surface is.

Remember, if you can see it, make it look good.